The Mastiff, an ancestor to many modern purebred dogs, is a very important breed. They likely date as far back as ancient Egyptian and Chinese civilizations. Mastiffs are very large dogs, with the average weight being between 175 and 200 pounds. Caesar praised the Mastiff for its fighting ability and Mastiffs were introduced to England by Phoenician sailors in the sixth century. The breed was often used in the blood sports of bear-baiting, bull-baiting, and dog fighting.

Mastiffs are known for protecting their masters and property, especially from wolves. Legend has it that at the Battle of Agincourt in 1415, a Mastiff defended his wounded master for many hours until he could be rescued. The Mastiff likely made its way to America on the Mayflower; however no significant numbers were imported to the United States until the late 1800's. After Britain passed laws that banned baiting sports the breed became less popular, and after World War II was facing extinction.

Proponents of the breed were able to preserve it thanks to its presence outside Europe, most notably in the United States. The Mastiff was recognized by the American Kennel Club in 1885.